The interactions of human complement with interfacially aggregated preparations of human secretory IgA

The effects of human saliva on the hemolytic activity of complement

Human saliva was tested for the presence of factors that affect the complement system. Parotid saliva and salivary fractions were incubated at 37 C with human serum as a source of complement. Samples removed from the mixtures within the first 15 minutes had higher levels of whole hemolytic complement activity than did appropriate controls. The final ionic strength of the saliva-serum mixtures was critical to the hemolytic activity of complement. After 60 minutes all serum-saliva mixtures had lower levels of hemolytic activity than did serum-buffer controls. With regard to whole saliva, the salivary sediment was found to be strongly complement-reactive.

Detection of functional complement components in gingival crevicular fluid from humans with periodontal diseases

Crevicular fluid was collected from patients with periodontitis by a capillary tube procedure. Complement component activities were determined by functional assay systems, with human complement, and partially purified human first complement component (C1) as controls. The complement-fixing properties of the dental plaque of each patient were also examined C1 activity in the crevicular fluid of all patients was approximately 1/8 of whole serum C1 and diminished rapidly with time after collection. There was no significant relationship between C1 concentration and crevicular fluid flow rate. Hemolytic activity of whole complement was also invariable detected when sufficient amounts (8 micronl) of crevicular fluid could be obtained. Dental plaque was found to fix C1. A role for crevicular complement in inflammatory periodontal disease is suggested.

Nephritic factor: Description of a new quantitative assay and findings in glomerulonephritis

A sensitive quantitative test for nephritic factor (NF) in human serum is reported. The test is based on the capacity of NF to initiate fluid phase consumption of the third complement (C) component in the presence of magnesium ions (Mg++) and of factors of the alternative pathway of C activation. These factors as well as C3 and C5 were supplied by the incorporation of normal human serum (NHS) into the assay mixture. In order to prevent C3 (and C5) consumption via the Ca++- and Mg++-dependent classical pathway, the test was performed in the presence of the chelating agent Mg-ethylene bis (oxyethylene-nitrilo) tetraacetic acid (Mg EGTA) which interacts preferentially with Ca++. The Mg EGTA concentration was found to be critical, a final concentration of 5 mM in the assay mixture being required for optimal results. By its heat stability (54 degrees to 56 degrees C, 30 min), NF could be distinguished from other, heat-labile NF-like factors. The NF test was applied to five categories of patients with glomerulonephritis (GN). Heat-stable NF activity was found in seven of 17 sera in the membranoproliferative glomerulonephritis (MPGN) group. Two of the 12 acute poststreptococcal GN sera had NF-like activity which disappeared upon heating. Serum C3 and proactivator (PA) concentrations varied widely in all groups but a clear positive relationship was found between the presence of NF and low serum C3 concentrations in MPGN. Renal immunofluorescence in MPGN indicated a lesser amount of lg deposited in glomeruli from patients with NF when compared to the NF-negative patients. Both groups had heavy C3 deposits. The availability of a sensitive, quantitative assay for NF may help to provide further insight into the various pathogenic mechanisms in different forms of MPGN.

Detection and differentiation of immune complexes and IgG aggregates by a complement consumption assay

The applicability of a complement consumption assay as a means by which to detect IgG aggregates and immune complexes in serum was examined. Both heavy (greater than or equal to 19S) and intermediate (11-17S) IgG aggregates were detected and the sensitivity of the assay was greater than or equal to 10 mug aggregated IgG/ml. BSA anti-BSA complexes, formed in slight antibody excess, were detected at a BSA concentration of 200 ng/ml. NHS stored at 4degreesC for greater than or equal to 2-3 weeks or at -20degreesC for more than 3 months developed distinct anticomplementarity (AC). This background AC, due to IgG aggregate formation, was reduced by heating the serum at 56degreesC for 50 min prior to testing. A similar reduction of AC and C1q fixation was observed when IgG aggregated at 61degreesC or 63degreesC was heated further at 56degreesC for 50 min. The abatement of AC could not be correlated to a change in IgG aggregation size. In contrast, AC of preformed antigen-antibody complexes was not reduced by this heat treatment.

Immune components in dental plaque

Acquired pelicle appears to contain primarily IgA and other proteins of salivary origin. With the increased time necessary for plaque formation, gingival crevicular fluid contributes proteins to the growing plaque accumulation. However, secretory IgA is still the major intact immunoglobulin in plaque samples since appreciable portions of the molecules bearing IgG determinants appear to be degraded to small fragments. Nevertheless, the amount of IgA present in plaque, which could be considered antibody, is too little to account for most of the plaque interactions. Since secretory IgA appears to be resistant to proteolytic degradation by a mixture of plaque enzymes, and IgA fragments are not prominent in plaque extracts, degradation of secretory IgA probably cannot explain the relatively low IgA levels in plaque. It has been shown that salivary IgA antibody can interfere with enzymes responsible for the plaque-forming potential of certain organisms. All the preceding evidence is consistent with our current contention that secretory IgA functions as blocking antibody to interfere with the formation of dental plaque. This could occur by direct inhibition of bacterial polymer formation or by direct or indirect inhibition of bacterial interaction with salivary constituents by secretory IgA. Less than 1% of the plaque interactions can probably be attributed to secretory IgA antibody. IgG may contribute even less since it is degraded.

A Clq immunosorbent assay compared with thin-layer gel filtration for measuring IgG aggregates

A new sensitive technique measures C1q-binding of human IgG aggregates. The method is based on the principle of the enzyme-linked immunosorbent assay with C1q-coated tubes. The IgG aggregates attaching to this C1q are shown by enzyme-linked anti-human IgG. Less than 0.01 mug of aggregates per milliliter of sample can be detected. The results with this new method showed significant correlation (P less than 0.01; Spearman rank correlation test) with the estimates of IgG aggregates of 13S or more and 10S in size obtained by thin-layer gel filtration. Both of these methods showed significant correlation with the classic hemolysis inhibition method for measuring complement fixation.

IgA in commercial gamma-globulin preparations

The presence of anti-IgA has been related to adverse reactions to injection or infusion of IgA-containing material. In this study IgA was demonstrated in all of the investigated commercial gamma-globulin preparations. In the material from a few producers it was, however, very low. By immuno-gel filtration it could be shown that the IgA consisted of aggregates as well as a 7S component and fragments. By immunoelectrophoresis-immunofluorescence IgG-IgA complexes could also be detected. The IgA aggregates could be almost completely degraded by reduction-alkylation. It is implied that such changed IgA in gamma-globulin preparations for injection may increase the risk of immunization against IgA.